Activator solution is a combination of 50% propylene glycol and 50% distilled water mixture.
The primary reason this is used over tap water is that the solution is void of impurities that regular tap water may contain. These impurities can negatively affect the humidor as tap water can breed mold and unwanted odor. Activator solution also assists in preventing cigars from molding and maintains a 70% environment in your humidor.

Using the 50/50 solution on your humidifier is fairly simple and straightforward:

1. Simply place your humidifier on a table with a cloth underneath it.

2. Then, open the activator bottle and generously add the  solution into the humidifier. You don't want to drench the humidifier, but rather make moist (without excess water dripping out).

3. Be sure to remove the excess liquid, wipe clean with a cloth and place it back into your humidor.

This procedure should be repeated on average every 60 days or when your hygrometer indicates a lower humidity level that is desired.